1. Field of the Invention
The present invention relates to a novel polyimide, a process for preparing the polyimide, a novel aromatic diamino compound used for preparing the polyimide, and a process for preparing the aromatic diamino compound. More particularly, the invention relates to a novel, thermoplastic and amorphous polyimide which is readily soluble in organic solvents and a process for preparing the polyimide.
The novel aromatic diamino compound of the invention is useful for preparing the polyimide of the invention and can also be used as a raw material for other polyimides, polyamides, polyamideimides, bismaleimides and epoxy resins, and as a curing agent for other maleimide compounds and epoxy compounds.
The present invention further relates to a soluble and thermoplastic polyimide-based resin composition, a process for preparing the resin composition and an injection molded article of the resin composition. More particularly, the invention relates to a polyimide-based resin composition comprising a thermoplastic polyimide having good solubility in general purpose organic solvents and a fibrous reinforcement such as carbon fiber, glass fiber, aromatic polyamide fiber and/or a potassium titanate fiber; a process for preparing the polyimide base resin composition; and an injection molded article prepared from the polyimide-based resin composition.
The present invention more further relates to a polyimide-based composite, and more particularly relates to a polyimide-based laminated composite obtained by molding the above soluble and thermoplastic polyimide in combination with a fibrous reinforcement and a process for molding the same.
The present invention still further relates to a fibrous reinforcement having a surface modified with the above polyimide.
The fibrous reinforcement having a surface modified with the above polyimide which can be used for the invention has an improved applicability. That is, polyimide used for the invention can be applied as a surface modifier for the fibrous reinforcement particularly in the form of a solution.
2. Related Art of the Invention
Recently, materials composed of heat resistant resin have been required to satisfy thermal and mechanical properties as well as flexibility in a composite. The material are also required to have other properties such as processability.
Polyimide resin has received attention as a material that can satisfy these requirements.
Conventionally, polyimide has been excellent in mechanical properties, chemical resistance, flame retardance and electrical properties in addition to its essentially excellent heat resistance. Consequently, polyimide has been widely used in many fields such as processing materials, composite materials and electric and electronic devices.
However, polyimide resin has the disadvantage of poor processability. A typically known polyimide is, for example, an aromatic polyimide prepared from 4,4'-diaminodiphenyl ether and pyromellitic dianhydride and having recurring structural units of the formula (A): ##STR3## (Trade Mark :Kapton and Vespel, manufactured by E.I. Du Pont de Nemours & Co.). The polyimide is insoluble and infusible and must be molded by special techniques such as sintering of powder. Molded articles having complex shapes are difficult to obtain by the technique and sintered products must be further finished by cutting or other operations to obtain satisfactory articles. Thus, the polyimide has a great disadvantage of high processing cost and cannot be used for polyimide varnish. Consequently, research and development on soluble or fusible (thermoplastic) polyimide has been extensively carried out in order to provide processability for polyimide.
Soluble polyimide is expected in the future to be used for heat resistant varnish, coating and sealant. Solubilizing methods are summarized, for example, in "Polyimide Resin" published by Technical Information Association (1991). The methods include an increase in the molecular chain flexibility by introducing a flexible bond or by conducting copolymerization and increasing the mutual action with a solvent by introducing an alkyl group. Most of the soluble polyimides, however, can be soluble only in high boiling point solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide and cresol as disclosed in, for example, Japanese Laid-Open Patent Sho 61-130342. The soluble polyimide also has a problem of containing a sulfonyl group which has a high moisture absorption. A series of recent Japanese Laid-Open Patents has disclosed polyimide which is soluble in low boiling point solvents such as acetone, toluene and dichloromethane. Such polyimide, however, has a disadvantage that an alkyl group having poor heat resistance is present in the molecular chain as disclosed in, for example, Japanese Laid-Open Patent Hei 1-263116, 1-263117 and 2-160832.
On the other hand, various soluble (thermoplastic) polyimides have also been developed. For example, an improvement of the raw material diamine component has also been tried to improve in order to eliminate the above disadvantage.
Polyimide has been known to be capable of having its transition temperature and melt flowability controlled by changing a bonding radical in the monomer units or by introducing a folded structure into the molecule. For example, polyimide LARC TPI from NASA is prepared from 3,3'-diaminobenzophenone and benzophenonetetracarboxylic dianhydride and has a fundamental skeleton of the formula (B) below. The polyimide has been further improved and thermoplastic polyimide has been developed by reacting 1,3-bis(3-aminobenzoyl)benzene with various tetracarboxylic dianhydrides (Japanese Patent Application Hei 03-223930).
Such polyimide exhibits excellent heat resistance and adhesive property. On the other hand, the melt flow property is still insufficient and the polyimide is primarily used in the form of polyamic acid varnish. Such varnish has a difficulty in treating the moisture formed in the final step of hot ring-closure from polyamic acid to polyimide, and leads to a problem of void generation in the adhesive layer.
As a result, it is a disadvantage that the desired property is difficult as an exhibit and the application step to adhesive is complex.
The present inventors have controlled the molecular weight of the polymer having the fundamental skeleton of the formula (B): ##STR4## by capping the reactive end of the polymer chain and found polyimide which can be injection molded and extruded as disclosed in Japanese Laid-Open Patent Hei 2-018419.
The polyimide powder thus obtained, however, has a melting point of around 340.degree. C. and must be converted to amorphous form in order to use the powder for processing or adhesion.
Further, the polyimide of the above formula (B) can be used for an adhesive having excellent heat resistance and is now primarily used for adhesion of metals, prepregs, ceramics and polyimide films of FPC base material and is expected to develop in a further broad field of adhesive by making the best use of the excellent thermoplasticity.
Polyimide has been conventionally applied for adhesive purposes by the following methods.
1) Varnish of polyamic acid precursor is applied to an adhesive surface and hot-pressed to perform adhesion through solvent removal and imidization. PA0 2) A polyimide film is inserted between adhesive surfaces and hot-pressed to perform adhesion. PA0 3) Polyimide powder is suspended in a volatile solvent, successively applied to the adhesive surface, subjected to solvent removal by evaporation and hot-pressed to perform adhesion. PA0 1) A polyimide comprising a requisite structural unit consisting of one or more recurring structural units of the formula (1): ##STR5## wherein m and n are individually an integer of 0 or 1, and R is ##STR6## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are individually a hydrogen atom, halogen atom, alkyl having 1 to 8 carbon atoms, aryl, alkenyl, aralkyl or alkoxy having 1 to 5 carbon atoms; R.sub.5, R.sub.6 and R.sub.7 are individually a hydrogen atom, alkyl having 1 to 8 carbon atoms, aryl, alkenyl, aralkyl or .omega.-alkyloxyoligo(alkyleneoxy)alkyl having 1 to 10 carbon atoms and 1 to 3 oxygen atoms; and Ar is a tetravalent radical having 2 to 27 carbon atoms and being selected from group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected to each other with a direct bond or a bridge member. PA0 2) A polyimide comprising a requisite structural unit consisting of one or more recurring structural units of the formula (1): ##STR7## wherein m, n, R and Ar are the same as above, and having at the polymer chain end thereof an aromatic ring which is essentially unsubstituted or substituted with a radical having no reactivity with amine and/or dicarboxylic anhydride. PA0 3) A polyimide of 1) or 2) wherein the polyimide having recurring structural units of the formula (1) is derived from a precursor polyamic acid having an inherent viscosity of 0.01 to 3.0 dl/g at 35.degree. C. in a dimethylacetamide solution at a concentration of 0.5 g/dl. PA0 4) A polyimide of 1) or 2) wherein the polyimide having recurring structural units of the formula (1) has an inherent viscosity of 0.01 to 3.0 dl/g at 35.degree. C. at a concentration of 0.5 g/dl in a solvent mixture composed of 9 parts by weight of p-chlorophenol and 1 part by weight of phenol. PA0 5) A polyimide comprising a requisite structural unit consisting of one or more recurring structural units of the formula (2): ##STR8## wherein m and n are individually an integer of 0 or 1, R.sub.8 is a hydrogen atom, halogen atom, alkyl having 1 to 4 carbon atoms, alkoxy or phenyl, and Ar is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected to each other with a direct bond or a bridge member. PA0 6) A polyimide comprising a requisite structural unit consisting of one or more recurring structural units of the formula (2) : ##STR9## wherein m, n, R.sub.8 and Ar are the same as above, and having at the polymer chain end thereof a radical which is essentially unsubstituted or substituted with a radical having no reactivity with amine and/or dicarboxylic anhydride. PA0 7) A polyimide comprising a requisite structural unit consisting of one or more recurring structural units selected from the group consisting of 1 the units of the formula (3); ##STR10## wherein R.sub.9 is ##STR11## and Ar is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected to each other with a direct bond or a bridge member, PA0 8) A polyimide copolymer comprising a requisite structural unit consisting of 1 to 99% by mol of recurring structural units of the formula (1): ##STR14## wherein m, n, R and Ar are the same as above, 99 to 1% by mol of recurring structural units of the formula (6): ##STR15## wherein n is an integer of 0 to 5, Q is a direct bond, --O--, --S--, --CO--, --SO.sub.2 --, --CH.sub.2 --, --C(CH.sub.3).sub.2 -- or --C(CF.sub.3).sub.2 -- and may be the same or different when aromatic rings are connected to each other with two or more connecting radicals Q, and Ar' is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected to each other with a direct bond or a bridge member, or said polyimide copolymer having at the polymer chain end a radical which is essentially unsubstituted or substituted with a radical having no reactivity with amine and/or dicarboxylic anhydride. PA0 9) A polyimide copolymer comprising a requisite structural unit consisting of 1 to 99% by mol of recurring structural units of the formula (2): ##STR16## wherein m and n are individually an integer of 0 or 1, R.sub.8 is a hydrogen atom, halogen atom, alkyl of 1 to 4 carbon atoms, alkoxy or phenyl, and Ar is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected to each other with a direct bond or a bridge member, and 99 to 1% by mol of recrring structural units of the formula (6): ##STR17## wherein n, Q and Ar' are the same as above, or said polyimide copolymer having at the polymer chain end a radical which is essentially unsubstituted or substituted with a radical having no reactivity with amine and/or dicarboxylic anhydride. PA0 10) A polyimide copolymer comprising two or more recurring strutural units of the formula (1) described in claim 1 or said polyimide copolymer having at the polymer chain end a radical which is essentially unsubstituted or substituted with a radical having no reactivity with amine and/or dicarboxylic anhydride. PA0 11) A process for preparing a polyimide having a requisite structural unit consising of one or more recurring structurel units of the formula (1): ##STR18## wherein m, n, R and Ar are the same as above, comprising reacting aromatic diamine essentially consisting of one or more aromatic diamino compounds of the formula (7): ##STR19## wherein m, n and R are the same as above, with tetracarboxylic dianhydride primarily having the formula (8): ##STR20## wherein Ar is a tetravalent radical having 2 to 27 carbon atoms and being selected from the group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected to each other with a direct bond or a bridge member, and thermally or chemically imidizing the resultant polyamic acid. PA0 12) A process for preparing a polyimide having a requisite structural unit consisting of one or more recurring structural units of the formula (1): ##STR21## wherein m, n, R and Ar are the same as above, and having at the polymer chain end a radical which is essentially unsubstituted or substituted with a radical having no reactivity with amine and/or dicarboxylic anhydride, comprising reacting aromatic diamine essentially consisting of one or more of aromatic diamino of the formula (7): ##STR22## wherein m, n and R are the same as above, with tetracarboxylic dianhydride primarily having the formula (8): ##STR23## wherein Ar is the same as above, in the presence of aromatic dicarboxylic anhydride of the formula (9): ##STR24## wherein Z is a divalent radical having 6 to 15 carbon atoms and being selected from the group consisting of a monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected to each other with a direct bond or a bridge member, and/or aromatic monoamine of the formula (10): EQU Z.sub.1 --NH.sub.2 ( 10) PA0 13) An aromatic dinitro compound of the formula (11); ##STR25## wherein m, n and R are the same as in the formula (1). 14) An aromatic diamino compound of the formula (7): ##STR26## wherein m, n and R are the same as in the formula (1). 15) An aromatic diamino compound of the formula (12): ##STR27## wherein n is an integer of 0 or 1, and R.sub.8 is a hydrogen atom, halogen atom, alkyl of 1 to 4 carbon atoms, alkoxy or phenyl. PA0 16) An aromatic diamino compound of the formula (13): ##STR28## wherein R.sub.9 is ##STR29## 17) An aromatic diamino compound of the formula (14): ##STR30## wherein R.sub.9 is the same as above. 18) An aromatic diamino compound of the formula (15): ##STR31## wherein R.sub.9 is the same as above. PA0 20) A process for preparing an aromatic diamino compound of the formula (7): ##STR32## wherein m and n are individually an integer of 0 or 1, and R is ##STR33## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are individually a hydrogen atom, halogen atom, alkyl having 1 to 8 carbon atoms, aryl, alkenyl, aralkyl or alkoxy having 1 to 5 carbon atoms; R.sub.5, R.sub.6 and R.sub.7 are individually a hydrogen atom, alkyl having 1 to 8 carbon atoms, aryl, alkenyl, aralkyl or .omega.-alkyloxyoligo(alkyleneoxy)alkyl having 1 to 10 carbon atoms and 1 to 3 oxygen atoms; and Ar is a tetravalent radical having 2 to 27 carbon atoms and being selected from group consisting of an aliphatic radical, alicyclic radical, monoaromatic radical, condensed polyaromatic radical and noncondensed aromatic radical connected to each other with a direct bond or a bridge member, comprising carrying out condensation of a dinitro compound of the formula (16): ##STR34## wherein X is a halogen atom, and m and n are individually an integer of 0 or 1, and a hydroxy compound of the formula (17): EQU R--OH (17)
The method 3) is particularly advantageous in view of simple procedures and is often used. Development of polyimide which can be applied to the method has been desired.
It is clear in the method that adhesion cannot be performed unless the melting point of the polyimide powder is exceeded.
In many research experiments, polyimide powder was suspended in a solvent, a prepreg was prepared by impregnating the suspension into a carbon cloth, and a composite was prepared from the prepreg and used for a structured material. In such procedures, a processing temperature exceeding the melting point of polyimide is required as in the case of the above method 3).
Thus, development of polyimide having good solubility and fusibility has been strongly desired in view of processing temperature and adhesion temperature.
Provision of polyimide having increased solubility in organic solvents or having a decreased melting point due to conversion of the polyimide powder from crystalline structure to amorphous structure as a substitute for polyimide of the formula (B) which is essentially excellent in various properties while insoluble in almost organic solvents has a great contribution to the improvement of processability and adhesive property of polyimide, extension of fields of use, and improvement and rationalization of application methods.
However, the polyimide has also poor solubility in the general purpose organic solvents although thermoplasticity is provided, and thus it has been difficult to impregnate fibrous reinforcements with a solution of the polyimide.
Further, the polyimide has led to the above problems because of low resistance to water and moisture absorption as compared with conventional engineering plastics.
One of the techniques utilizing the heat resistance and mechanical strengths of polyimide is to apply the polyimide in the form of a composite material in combination with glass fiber or carbon fiber. Non-thermoplastic polyimide is usually applied to such process. A fibrous material is generally impregnated with a solution of polyamic acid precursor of the polyimide, the solvent is removed by evaporation and thereafter imidization and curing are simultaneously carried out by hot compression molding (Japanese Laid-Open Patent SHO 60-240740 and 61-235437). The process, however, requires to carry out imidization and molding at the same time and is liable to emerge voids and other defects due to water generated by imidization.
Utilization of thermoplastic polyimide has been proposed as a countermeasure against these difficulties (Japanese Laid-Open Patent HEI 01-113461 and 03-199234). In such a case, however, polyimide is insufficient in melt-flowability though heat-resistant and thermoplastic, and it has been found difficult to completely inhibit generation of voids and other defects as in the above process of using polyamic acid.
As mentioned above, known polyimide has problems of water generated in the imidization step, although good impregnation of fibrous materials can be carried out by using the solution of polyamic acid precursor even in the case of non-thermoplastic polyimide.
On the other hand, thermoplastic polyimide has no problem of generating water and other low molecular weight substances.
However, flowability of polyimide is unsatisfactory, fibrous materials can not be fully impregnated with polyimide, and thus it has been difficult to obtain molded articles having excellent properties.
Fibrous reinforcements which are used for various resin composites are modified on the surface depending upon the kind of resin to be reinforced in order to enhance compatibility with the resin and to improve properties of the composite obtained.
For example, carbon fiber is excellent in high elasticity and light-weight properties in a variety of fibrous reinforcement is very suited for a reinforcement of super heat resistant resins such as polyimide, polyether ether ketone, polyether sulfone, polyetherimide and polyphenylene sulfide, improves mechanical strength and other properties, and can be used as an excellent material of automotive and machinery parts.
Conventionally, it has been widely known to modify a surface of carbon fiber with epoxy resin. Epoxy resin, however, is effective as a surface modifier for a matrix of thermosetting resin such as epoxy resin whereas often has poor adhesion to a matrix of thermoplastic resin. Thus, carbon fiber modified with epoxy resin has not sufficiently improved mechanical strength and other properties of molded articles. As a result, polyamide resin has been tried to use as a surface modifier of carbon fiber and other fibrous reinforcements for the matrix of thermoplastic resin in Japanese Laid-Open Patent SHO 53-106752.
However, in the case of using super heat-resistant thermoplastic resin as a matrix, molding is conducted at a high temperature exceeding 300.degree. C. and thus the surface modifier of polyamide resin is heat decomposed in the course of molding and leads to problems such as formation of voids and reduction of weld strength. Polyimide resin has not provided a satisfactory surface modifier. On the other hand, it has been proposed to use polyether imide resin and polyimide resin which have excellent heat resistance as surface modifiers for solving the above problem of heat decomposition in Japanese Laid-Open Patent SHO 62-299580 and 64-40569. However, problems have been found concerning the adhesion between these resins and the matrix of thermoplastic resin. A surface modifier and a surface-modified fibrous reinforcement which can sufficiently exhibit modification effect have not yet been found.